Surface processes controlling MBE heterojunction formation: GaAs(100)/Ge interfaces

Abstract

In situ LEED and synchrotron radiation photoemission spectroscopy were performed on Ge interfaces grown by MBE on GaAs(100) surfaces ranging from the As-rich c(4×4) to the Ga-rich 4×6 ordered MBE surface phases. By comparison to MBE and bulk grown c-GeAs, we find that when lattice-matched heterojunctions are grown on GaAs surfaces, GeAs forms an ordered 3×1 phase at the free surface of Ge(110) and a two-domain (2×1) phase at the free surface of Ge(100). The GeAsx two-domain (2×1) ordered Ge(100): As surface phase is obtained independent of the initial GaAs(100) surface As concentration. Further, As outdiffusion does not occur during the initial deposition of Ge; rather, we observe an As enrichment of the Ge surface at a Ge coverage corresponding to the initial surface As concentration. The As diffusion from the interface layer, while lowering the free energy of the Ge surface layers, also changes the band-gap offset.